Optical transmission system, optical transmission apparatus and optical transmission method

Abstract

An optical transmission system includes a plurality of transmission lines through which a mode-multiplexed signal obtained by multiplexing a plurality of optical signals of different types of modes is transmitted, and one or more mode group permutation units provided between the plurality of transmission lines. The mode group permutation unit changes, on a mode-group-by-mode-group basis, an optical signal of a mode belonging to a mode group to an optical signal of another mode belonging to a mode group after permutation corresponding to the mode group in such a manner that modes are interchanged between at least some of the plurality of optical signals multiplexed into the mode-multiplexed signal input from one of the plurality of transmission lines on an input side, and outputs the mode-multiplexed signal after mode interchange to one of the plurality of transmission lines on an output side.

The invention claimed is: 
     
       1. An optical transmission system comprising:
 a plurality of transmission lines through which a mode-multiplexed signal obtained by multiplexing a plurality of optical signals of different types of modes is transmitted; and 
 one or more mode group permutation units provided between the plurality of transmission lines, wherein 
 each of the one or more mode group permutation units changes, on a mode-group-by-mode-group basis, an optical signal of a mode belonging to a mode group to an optical signal of another mode belonging to a mode group after permutation corresponding to the mode group in such a manner that the modes are interchanged between at least some of the plurality of optical signals multiplexed into the mode-multiplexed signal input from one of the plurality of transmission lines on an input side, and outputs the mode-multiplexed signal after mode interchange to one of the plurality of transmission lines on an output side, 
 at least one of the one or more mode group permutation unit includes:
 a mode demultiplexer configured to separate the optical signals of a plurality of types of modes multiplexed into the mode-multiplexed signal input from the transmission line on the input side, 
 mode group permutation devices corresponding to a plurality of mode groups, and 
 a mode multiplexer configured to output a mode-multiplexed signal obtained by multiplexing the optical signals of a single mode output from the mode group permutation devices corresponding to the plurality of mode groups to the transmission line on the output side, and 
 
 each of the mode group permutation devices receives, from the mode demultiplexer, the optical signals of modes belonging to the mode group before permutation corresponding to the mode group permutation device, changes a mode of at least some of the received optical signals to another mode belonging to a mode group after permutation corresponding to the mode group permutation device, and outputs the optical signals after mode change to the mode multiplexer. 
 
     
     
       2. The optical transmission system according to  claim 1 , wherein
 the mode group before permutation and the mode group after permutation corresponding to the mode group before permutation are identical. 
 
     
     
       3. The optical transmission system according to  claim 1 , wherein
 the mode group before permutation and the mode group after permutation corresponding to the mode group before permutation are different. 
 
     
     
       4. The optical transmission system according to  claim 1 , wherein
 the mode group before permutation and the mode group after permutation corresponding to the mode group before permutation are different, and the mode before change and the mode after change constitute a combination having a large difference in propagation constant. 
 
     
     
       5. The optical transmission system according to  claim 1 , wherein
 each of the mode groups is a first order mode group including a mode of a first order mode or a second order mode group higher than the first-order mode group including a mode of a second order mode higher than the first-order mode. 
 
     
     
       6. An optical transmission apparatus comprising:
 a mode group permutation unit configured to receive a mode-multiplexed signal obtained by multiplexing a plurality of optical signals of different types of modes from a transmission line on an input side, changes, on a mode-group-by-mode-group basis, an optical signal of a mode belonging to a mode group to an optical signal of another mode belonging to a mode group after permutation corresponding to the mode group in such a manner that the modes are interchanged between at least some of the plurality of optical signals multiplexed into the received mode-multiplexed signal, and outputs the mode-multiplexed signal after mode interchange to a transmission line on an output side, 
 wherein the mode group permutation unit includes:
 a mode demultiplexer configured to separate the optical signals of a plurality of types of modes multiplexed into the mode-multiplexed signal input from the transmission line on the input side, 
 mode group permutation devices corresponding to a plurality of mode groups, and 
 a mode multiplexer configured to output a mode-multiplexed signal obtained by multiplexing the optical signals of a single mode output from the mode group permutation devices corresponding to the plurality of mode groups to the transmission line on the output side, and 
 
 each of the mode group permutation devices receives, from the mode demultiplexer, the optical signals of modes belonging to the mode group before permutation corresponding to the mode group permutation device, changes a mode of at least some of the received optical signals to another mode belonging to a mode group after permutation corresponding to the mode group permutation device, and outputs the optical signals after mode change to the mode multiplexer. 
 
     
     
       7. An optical transmission method in an optical transmission system including a plurality of transmission lines through which a mode-multiplexed signal obtained by multiplexing a plurality of optical signals of different types of modes is transmitted, and one or more mode group permutation units provided between the plurality of transmission lines, the optical transmission method comprising:
 by each of the one or more mode group permutation units, changing, on a mode-group-by-mode-group basis, an optical signal of a mode belonging to a mode group to an optical signal of another mode belonging to a mode group after permutation corresponding to the mode group in such a manner that the modes are interchanged between at least some of the plurality of optical signals multiplexed into the mode-multiplexed signal input from one of the plurality of transmission lines on an input side, and outputting the mode-multiplexed signal after mode interchange to one of the plurality of transmission lines on an output side including:
 separating the optical signals of the plurality of types of modes multiplexed into the mode-multiplexed signal input from the transmission line on the input side, and 
 outputting a mode-multiplexed signal obtained by multiplexing the optical signals of a single mode output from mode group permutation devices corresponding to a plurality of mode groups to the transmission line on the output side, and 
 receiving the optical signals of modes belonging to the mode group before permutation corresponding to the mode group permutation device and changing a mode of at least some of the received optical signals to another mode belonging to a mode group after permutation corresponding to the mode group permutation device, and outputting the optical signals after mode change.